1. Field of the Invention
This invention relates to a method and apparatus for forming a glass sheet and, more particularly, to a method and apparatus wherein forming occurs while the glass sheet is being transported on a rotating forming surface.
2. Description of the Related Art
In the art of forming glass sheets into finished products of complex shape, there are few known methods of transporting the glass sheet to and through a forming or shaping operation after it has been heated to the softening point, i.e., to a temperature sufficiently high that it may be formed.
A first known manner of transporting a heated glass sheet is by gripping an upper edge thereof with tongs. This method leaves marks in the upper edge of the glass sheet and generally does not work well on a relatively thin glass sheet.
A second method of transporting a heated glass sheet is on a metal ring which engages the periphery of the glass sheet. This transportation method tends to leave marks along the edges of the glass sheet. There is also no full, direct surface dimensional control of the shape of the formed glass sheet if the glass sheet remains supported by the metal ring during a shaping operation, because the ring contacts only the periphery of the glass.
A third method of transporting a heated glass sheet during a shaping operation is on a cushion of gas, such as in the well known "Gas Hearth" process, which is used typically only for bending a glass sheet into a cylindrical form. For other than cylindrical forms, the glass sheet is picked up from the air cushion and moved against a suitable shaping mold.
A fourth method of transporting a heated glass sheet is on ceramic rolls. Once again, some device must be used to pick the glass sheet up from the ceramic rolls and bring it into contact with a suitable forming die in order to form it into a product having a complex shape. Transportation of glass sheet on ceramic rolls generally is acceptable for a glass product which is to be used as a side lite for an automobile, for example. This method is not known to work satisfactorily, however, for the production of a windshield quality glass product or for a relatively thin glass product.
In all except the second method mentioned above to be known in the art for transporting a heated glass sheet in a glass shaping operation, the glass sheet is stopped in its transportation path and thereafter moved into engagement with some type of forming equipment. Thus, there is an interruption in the glass forming process which adds time, complexity and cost to the forming process. One complexity added by stopping the glass sheet is the need to determine or at least estimate the degree of cooling of the glass during the stop and to compensate for such cooling in the heating of the glass sheet.
It is an object of this invention to provide a method and apparatus for forming a glass sheet in which the sheet can be formed while continuously in motion from a heating operation through the forming operation. It is another object of this invention that forming of a glass sheet be carried out concurrently with the transportation of that glass sheet toward the end of a glass processing line. It is a further object of this invention, according to certain preferred embodiments, to provide a method and apparatus for forming a glass sheet with dimensional control over the entire surface area thereof.
These and other objects and features of the invention will be better understood in the light of the following disclosure and discussion thereof.